Electrostatographic imaging systems involve the formation and development of electrostatic latent images. In some such imaging systems, a photoconductive insulating layer is imaged by uniformly electrostatically charging its surface, followed by exposing the surface to a pattern of activating electromagnetic radiation such as light, thereby selectively dissipating the charge in the illuminated areas to cause a latent electrostatic image to be formed in the non-illuminated areas.
This latent electrostatic image can be developed with developer compositions containing toner particles, followed by transferring the developed image to a suitable substrate such as paper.
Many photoconductive members are known. For example, photoconductive insulating materials can be deposited on conductive substrates. They often contain a thin barrier layer of a charge blocking material such as aluminum oxide between the substrate and the photoconductive composition. The barrier layer is primarily for the purpose of preventing charge injection from the substrate into the photoconductive layer subsequent to charging, as injection could adversely affect the electrical properties of a photoconductive member.
Examples of photoconductive members include those comprised of a homogeneous layer of inorganic or organic photoconductive compositions, composite layered devices containing photoconductive substances dispersed in other materials, and the like. An example of one type of composite photoconductive layer is described, for example, in U.S. Pat. No. 3,121,006, which discloses finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. In one form, the photoconductive composition involved is comprised of a paper backing containing a coating thereon of a binder layer comprised of particles of zinc oxide uniformly dispersed therein. Useful binder materials disclosed include those which are incapable of transporting for any significant distance injected charge carriers generated by the photoconductive particles. The photoconductive particles must be in substantially contiguous particle to particle contact throughout the layer for the purpose of permitting charge dissipation for a cyclic operation. Thus, about 50 percent by volume of photoconductive particles is usually necessary in order to obtain sufficient photoconductor particle to particle contact for rapid discharge. These high photoconductive particle concentrations can destroy the physical continuity of the resin particles, thus significantly reducing the mechanical strength of the binder layer.
Illustrative examples of specific binder materials disclosed in U.S. Pat. No. 3,121,006 include, for example, polystyrene resins, silicone resins, acrylic and methacrylic ester polymers, polymerized ester derivatives of acrylic and alpha-acrylic acids, chlorinated rubber, vinyl polymers and copolymers, and cellulose esters.
In devices employing photoconductive binder structures which include inactive electrically insulating resin such as those described in U.S. Pat. No. 3,121,006, conductivity or charge transport is accomplished through high loadings of the photoconductive pigment and allowing particle-to-particles contact of the photoconductive particles. In the case of photoconductive particles dispersed in a photoconductive matrix, such as illustrated by U.S. Pat. No. 3,121,007, photoconductivity occurs through the generation and transport of charge carriers in both the photoconductive matrix and the photoconductive pigment particles.
Known photoconductive compositions include amorphous selenium, halogen doped amorphous selenium substances, amorphous selenium alloys, including selenium arsenic, selenium tellurium, selenium arsenic antimony, halogen doped selenium alloys, wherein the halogen may be chlorine, iodine, or fluorine, cadmium sulfide, and the like. Generally, these photoconductive materials are deposited on suitable conductive substrates in xerographic imaging systems.
Imaging members wherein the charge generating and charge transport functions are accomplished by discrete contiguous layers are also known, such as those described in U.S. Pat. No. 4,265,990. Photoresponsive materials containing a hole injecting layer overcoated with a hole transport layer, followed by an overcoating of a photogenerating layer, and a top coating of an insulating organic resin, are disclosed in U.S. Pat. No. 4,251,612. Examples of such photogenerating layers include trigonal selenium and phthalocyanines, while examples of such transport layers include certain aryl diamines. The disclosures of U.S. Pat. Nos. 4,265,990 and 4,251,612 are hereby totally incorporated herein by reference.
U.S. Pat. No. 3,574,181 discloses disazo compounds useful as coloring agents. These compounds include halogen substituents on the central aromatic groups.
Composite electrophotographic photosensitive materials containing various azo compounds are disclosed in U.S. Pat. No. 4,618,672, wherein diazo compounds particularly suitable for use in the charge generating layer of a layered electrophotographic photoconductor are illustrated.
U.S. Pat. No. 4,540,651 discloses an electrophotographic photosensitive member with high sensitivity which is capable of forming consistently good images. The member is comprised of a carrier generating layer and a carrier transporting layer on an electroconductive support. The carrier generating layer contains a diazo compound, and the carrier transporting layer contains a styryl compound and/or an amine derivative, a hydrazone compound or a carbazole derivative. Many diazo compounds used comprise a 2-hydroxy-3-naphthanilide coupler.
U.S. Pat. No. 4,612,271 discloses a photosensitive composition comprising azo compounds which can be applied to electrophotographic photoconductive materials. The azo compounds are comprised of a carboxamide with a polycyclo ring substituent containing a hydroxyl group bonded to the same ring as a chalcogen. The photosensitive composition is said to have an extremely high photosensitivity, and excellent chargeability.
U.S. Pat. No. 4,663,442 discloses a diazo compound for use as a charge generating material in a photosensitive layer of an electrophotographic element. The diazo compound has the general formula ##STR2## wherein Y represents a substituted or non-substituted cyclic hydrocarbon or a substituted or non-substituted heterocycle; R represents hydrogen, or a substituted or non-substituted phenyl group; and Z represents a substituted or non-substituted heterocycle fused with a phenyl nucleus.
U.S. Pat. Nos. 4,341,701 and 4,469,515 disclose a process for the synthesis of monoazo or diazo pigments. The method involves the combination of a coupling component and a diazonium and/or tetrazonium salt of an aromatic or heterocyclic amine. The resultant products of the combination are used to prepare the corresponding monoazo or diazo pigment. The products prepared in this fashion exhibit increased coloring strength, improved transparency and flow properties, and a higher degree of dispersibility.
U.S. Pat. No. 4,797,337 discloses photoconductive imaging members comprising a supporting substrate, a hole transport layer, and a photogenerating layer comprising disazo compounds selected from the group consisting of: ##STR3## wherein X is selected from the group consisting of: ##STR4## wherein Y is selected from the group consisting of: ##STR5## The photoconductive imaging members possess high cyclic stability, high photosensitivity, good dark development potential, low dark decay values and excellent panchromaticity. They are non-toxic and may be made inexpensively, which renders them disposable.